
slarrv.f(3) LAPACK slarrv.f(3)
NAME
slarrv.f 
SYNOPSIS
Functions/Subroutines
subroutine slarrv (N, VL, VU, D, L, PIVMIN, ISPLIT, M, DOL, DOU, MINRGP, RTOL1, RTOL2, W,
WERR, WGAP, IBLOCK, INDEXW, GERS, Z, LDZ, ISUPPZ, WORK, IWORK, INFO)
SLARRV computes the eigenvectors of the tridiagonal matrix T = L D LT given L, D and
the eigenvalues of L D LT.
Function/Subroutine Documentation
subroutine slarrv (integerN, realVL, realVU, real, dimension( * )D, real, dimension( * )L,
realPIVMIN, integer, dimension( * )ISPLIT, integerM, integerDOL, integerDOU, realMINRGP,
realRTOL1, realRTOL2, real, dimension( * )W, real, dimension( * )WERR, real, dimension( *
)WGAP, integer, dimension( * )IBLOCK, integer, dimension( * )INDEXW, real, dimension( *
)GERS, real, dimension( ldz, * )Z, integerLDZ, integer, dimension( * )ISUPPZ, real,
dimension( * )WORK, integer, dimension( * )IWORK, integerINFO)
SLARRV computes the eigenvectors of the tridiagonal matrix T = L D LT given L, D and the
eigenvalues of L D LT.
Purpose:
SLARRV computes the eigenvectors of the tridiagonal matrix
T = L D L**T given L, D and APPROXIMATIONS to the eigenvalues of L D L**T.
The input eigenvalues should have been computed by SLARRE.
Parameters:
N
N is INTEGER
The order of the matrix. N >= 0.
VL
VL is REAL
VU
VU is REAL
Lower and upper bounds of the interval that contains the desired
eigenvalues. VL < VU. Needed to compute gaps on the left or right
end of the extremal eigenvalues in the desired RANGE.
D
D is REAL array, dimension (N)
On entry, the N diagonal elements of the diagonal matrix D.
On exit, D may be overwritten.
L
L is REAL array, dimension (N)
On entry, the (N1) subdiagonal elements of the unit
bidiagonal matrix L are in elements 1 to N1 of L
(if the matrix is not splitted.) At the end of each block
is stored the corresponding shift as given by SLARRE.
On exit, L is overwritten.
PIVMIN
PIVMIN is REAL
The minimum pivot allowed in the Sturm sequence.
ISPLIT
ISPLIT is INTEGER array, dimension (N)
The splitting points, at which T breaks up into blocks.
The first block consists of rows/columns 1 to
ISPLIT( 1 ), the second of rows/columns ISPLIT( 1 )+1
through ISPLIT( 2 ), etc.
M
M is INTEGER
The total number of input eigenvalues. 0 <= M <= N.
DOL
DOL is INTEGER
DOU
DOU is INTEGER
If the user wants to compute only selected eigenvectors from all
the eigenvalues supplied, he can specify an index range DOL:DOU.
Or else the setting DOL=1, DOU=M should be applied.
Note that DOL and DOU refer to the order in which the eigenvalues
are stored in W.
If the user wants to compute only selected eigenpairs, then
the columns DOL1 to DOU+1 of the eigenvector space Z contain the
computed eigenvectors. All other columns of Z are set to zero.
MINRGP
MINRGP is REAL
RTOL1
RTOL1 is REAL
RTOL2
RTOL2 is REAL
Parameters for bisection.
An interval [LEFT,RIGHT] has converged if
RIGHTLEFT.LT.MAX( RTOL1*GAP, RTOL2*MAX(LEFT,RIGHT) )
W
W is REAL array, dimension (N)
The first M elements of W contain the APPROXIMATE eigenvalues for
which eigenvectors are to be computed. The eigenvalues
should be grouped by splitoff block and ordered from
smallest to largest within the block ( The output array
W from SLARRE is expected here ). Furthermore, they are with
respect to the shift of the corresponding root representation
for their block. On exit, W holds the eigenvalues of the
UNshifted matrix.
WERR
WERR is REAL array, dimension (N)
The first M elements contain the semiwidth of the uncertainty
interval of the corresponding eigenvalue in W
WGAP
WGAP is REAL array, dimension (N)
The separation from the right neighbor eigenvalue in W.
IBLOCK
IBLOCK is INTEGER array, dimension (N)
The indices of the blocks (submatrices) associated with the
corresponding eigenvalues in W; IBLOCK(i)=1 if eigenvalue
W(i) belongs to the first block from the top, =2 if W(i)
belongs to the second block, etc.
INDEXW
INDEXW is INTEGER array, dimension (N)
The indices of the eigenvalues within each block (submatrix);
for example, INDEXW(i)= 10 and IBLOCK(i)=2 imply that the
ith eigenvalue W(i) is the 10th eigenvalue in the second block.
GERS
GERS is REAL array, dimension (2*N)
The N Gerschgorin intervals (the ith Gerschgorin interval
is (GERS(2*i1), GERS(2*i)). The Gerschgorin intervals should
be computed from the original UNshifted matrix.
Z
Z is REAL array, dimension (LDZ, max(1,M) )
If INFO = 0, the first M columns of Z contain the
orthonormal eigenvectors of the matrix T
corresponding to the input eigenvalues, with the ith
column of Z holding the eigenvector associated with W(i).
Note: the user must ensure that at least max(1,M) columns are
supplied in the array Z.
LDZ
LDZ is INTEGER
The leading dimension of the array Z. LDZ >= 1, and if
JOBZ = 'V', LDZ >= max(1,N).
ISUPPZ
ISUPPZ is INTEGER array, dimension ( 2*max(1,M) )
The support of the eigenvectors in Z, i.e., the indices
indicating the nonzero elements in Z. The Ith eigenvector
is nonzero only in elements ISUPPZ( 2*I1 ) through
ISUPPZ( 2*I ).
WORK
WORK is REAL array, dimension (12*N)
IWORK
IWORK is INTEGER array, dimension (7*N)
INFO
INFO is INTEGER
= 0: successful exit
> 0: A problem occured in SLARRV.
< 0: One of the called subroutines signaled an internal problem.
Needs inspection of the corresponding parameter IINFO
for further information.
=1: Problem in SLARRB when refining a child's eigenvalues.
=2: Problem in SLARRF when computing the RRR of a child.
When a child is inside a tight cluster, it can be difficult
to find an RRR. A partial remedy from the user's point of
view is to make the parameter MINRGP smaller and recompile.
However, as the orthogonality of the computed vectors is
proportional to 1/MINRGP, the user should be aware that
he might be trading in precision when he decreases MINRGP.
=3: Problem in SLARRB when refining a single eigenvalue
after the Rayleigh correction was rejected.
= 5: The Rayleigh Quotient Iteration failed to converge to
full accuracy in MAXITR steps.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
September 2012
Contributors:
Beresford Parlett, University of California, Berkeley, USA
Jim Demmel, University of California, Berkeley, USA
Inderjit Dhillon, University of Texas, Austin, USA
Osni Marques, LBNL/NERSC, USA
Christof Voemel, University of California, Berkeley, USA
Definition at line 280 of file slarrv.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 slarrv.f(3) 
